A patent document 1 discloses a two-way linear solenoid valve used in a hydraulic control circuit of an automatic transmission.
This two-way linear solenoid valve is configured to control the opening amount of a pressure adjusting port communicating with a hydraulic circuit by the forward and backward movement in the axis direction of a spool. By this control of the opening amount of the pressure adjusting port to adjust the amount of oil flowing into a drain port from the pressure adjusting port, the oil pressure on a hydraulic circuit side is adjusted. However, in this type of the linear solenoid valve, there is possibility that if foreign substances (for example, sludge) are deposited inside the pressure adjusting port, the movement of the spool is inhibited by the foreign substances, and the oil pressure cannot be appropriately adjusted.
Therefore, a control device of this type of the linear solenoid valve is configured to execute the removing of the deposited foreign substances by operating (hereinafter, also referred to as a foreign substance removing operation) the spool in a predetermined mode, when the reduction of the oil pressure caused by the deposited foreign substances is determined.
When this foreign substance removing operation is performed, the control device sets the opening of the pressure adjusting port to be large for a predetermined time by maintaining the excitation current of the solenoid at a preset maximum valve and minimum value by every predetermined time. At this time, the flow amount of the oil discharged from the pressure adjusting port to the drain port increases, and the deposited foreign substances are discharged from the drain port together with the oil.
However, since, if the amount of the oil discharged from the drain port increases, there is possibility that output pressure is largely lowered, the operation mode to remove the foreign substances can be performed only when the reduction of the output pressure does not affect the automatic transmission. Therefore, it has been required that the removing of the foreign substances can be quickly performed at the time when the necessity of the removing of the foreign substances is confirmed,